Changes

From system integrators' perspective, eMMC's and SD cards are easier to use than raw NAND's because they hide most of the complexity regarding the management of the underlying memory. NonethelessOn the other hand, the architecture of these devices could make it difficult to retrieve data regarding the actual usage of the memory. There are some techniques available, however, to address this issue when working with an embedded Linux platform. This section will illustrate the following ones:* Logging the accesses to the storage device: The idea of this approach is to log all the accesses triggered by the host and isolate the write operations in order to determine the actual amount of data written onto the device. Two different methods are compared. The first one makes use of a hardware-based trace tracing tool while the other exploits a software tracer, namely the Linux kernel's Function Tracer (aka <code>ftrace</code>).

The evaluation kit consists of three boards: the SoM, the SBCX carrier board, and an adapter board. This setup provides off-chip trace via a parallel trace port or a PCIe interface. The SoM is equipped with the NXP i.MX8M SoC, which in turn is based on the Quad-Core Arm® ARM® Cortex-A53 CPU. The SOC features two Ultra Secured Digital Host Controller Controllers (uSDHC) supporting SD/SDIO/MMC cards and devices. For the purpose of the tests under discussion, the uSDHC ports were used as depicted in the following image.

[[File:MISC-TN-017-eMMC-uSD-interfacing.png|center|thumb|300px400x400px|eMMC and microSD card interfacing]]

The microSD card connected to uSDHC1 was used for the bootloader, the Linux kernel, and the root file system. The eMMC device connected to uSDHC2 was used for the main workload to be analyzed. The Linux kernel version used is 4.14.98.